1. Field of the Invention
The present invention relates to a secondary-battery internal short detection apparatus which detects an internal short being generated in a secondary-battery. It also relates, for the same purpose, to a secondary-battery internal short detection method, a battery-pack and electronic equipment.
2. Description of the Background Art
In a chemical battery such as a lithium-ion secondary-battery, a separator is provided which insulates each plate electrically between a positive electrode and a negative electrode. It also has the function of holding an electrolyte solution.
The difference in energy between the positive electrode and the negative electrode is naturally extracted to the outside as electrical energy. However, it is radiated to the outside as heat if the mixture of foreign matter or the like generates a short-circuit between the positive and negative electrodes. This short-circuit heat can heat the battery. Besides, once a short-circuit is produced, the generated heat may melt the separator. In the following cycles, the electrode plate is expanded and shrunk, or it is subjected to another such change. This can produce a short-circuit repeatedly, thus heating the battery further. Therefore, it is desirable that the fact that an internal short is generated in the battery be precisely detected. Then, if the internal short is generated, a processing should be executed for stopping using it or doing another such.
Conventionally, as the art of detecting an internal short, a power-source apparatus provided with a battery-abnormality decision apparatus is proposed which detects an instantaneous voltage drop when a short-circuit of positive and negative electrodes is produced in a lithium-ion battery (e.g., refer to Japanese Patent Laid-Open No. 2003-9405 specification). Or, a secondary-battery short-circuit detection method is suggested which detects a short-circuit being generated if a rise in the voltage at a charge time is below normal secondary-battery data acquired beforehand (e.g., refer to Japanese Patent Laid-Open No. 2002-50410 specification).
However, in terms of a notebook PC (or personal computer) or a cellular phone in which a secondary-battery is frequently used as its power-source, such equipment is often operated through a pulse charge and discharge for a short time. Hence, even in an ordinary secondary-battery, the voltage fluctuates at short time intervals. In addition, the period of time when a short-circuit is generated, or the depth of a drop in the voltage, varies. Accordingly, in the above described method of detecting an instantaneous voltage drop, only a drop in the voltage caused by a short-circuit is hard to distinguish. This may cause a false detection. Besides, in the above described method of making a comparison using ordinary secondary-battery data acquired in advance, a mass of data needs to be acquired according to changes in an electric current or temperature.